As semiconductor devices have been becoming finer in recent years, various material films having different properties are formed on a substrate, and are processed. In particular, in a damascene interconnect forming process in which interconnect trenches formed in a dielectric film are filled with a metal, an excessive metal is polished away by a polishing apparatus after a metal film is formed. Various films, such as a metal film, a barrier film, and a dielectric film, are exposed on a wafer surface that has been polished. Residues, such as slurry used in polishing and polishing debris, remain on these films that are exposed on the wafer surface. In order to remove these residues, the polished wafer is transported to a substrate cleaning apparatus, where the wafer surface is cleaned.
If cleaning of the wafer surface is insufficient, reliability problems, such as poor adhesion and a current leak due to the existence of the residues, may occur. Therefore, in manufacturing of a semiconductor device, cleaning of the wafer has been an important process for improving a yield of products.
As an apparatus for cleaning a substrate, there has been known a two-fluid cleaning apparatus that supplies a two-fluid jet, composed of a fluid mixture of a gas and a liquid, onto a surface of a substrate to thereby clean the substrate. As shown in FIG. 42, the two-fluid cleaning apparatus delivers the two-fluid jet from a two-fluid nozzle 500 onto a surface of a substrate W, while the two-fluid nozzle 500 is moved parallel to the surface of the substrate W, to generate shock waves by a collision between the two-fluid jet and the substrate W, thereby removing particles, such as abrasive grains and polishing debris, which exist on the surface of the substrate W.
However, as shown in FIG. 43, since the two-fluid jet reaches the substrate while spreading, an incident angle θ of the shock wave with respect to the substrate surface is small. As a result, as shown in FIG. 44, the shock waves do not impinge on particles existing in minute recesses on the substrate surface, thus failing to remove these particles.
FIG. 45 is a schematic view showing a structure of the two-fluid cleaning apparatus shown in FIG. 42. As shown in FIG. 45, a gas supply line 555 for supplying a gas into a gas pocket 560 formed in the two-fluid nozzle 500, and a liquid supply line 557 for supplying a liquid into a mixing chamber 561 formed in the two-fluid nozzle 500 are coupled to the two-fluid nozzle 500. The two-fluid nozzle 500 has a gas introduction port 564 at its upper portion, and the gas supply line 555 is coupled through this gas introduction port 564 to the two-fluid nozzle 500.
The liquid supply line 557 extends downwardly through the gas pocket 560 that is formed in the two-fluid nozzle 500. A liquid outlet 557a of the liquid supply line 557 is located in the two-fluid nozzle 500. The gas pocket 560 is located above the liquid outlet 557a of the liquid supply line 557, and the mixing chamber 561 is located below the liquid outlet 557a of the liquid supply line 557. The liquid, such as pure water, is supplied through the liquid supply line 557 into the mixing chamber 561 formed in the two-fluid nozzle 500.
The gas supply line 555 is provided with a gas supply valve 571 and a filter 572. The gas (e.g., inert gas, such as nitrogen gas) flowing in the gas supply line 555 passes through the gas supply valve 571 and the filter 572 in this order and further flows through the gas introduction port 564 into the gas pocket 560 of the two-fluid nozzle 500. The gas supply valve 571 may be a flow control valve (e.g., a mass flow controller), an air operated valve, an on-off valve, or the like.
The liquid and the gas are mixed in the mixing chamber 561 to form a high-pressure two-fluid mixture. During supplying of the gas into the gas pocket 560, as shown in FIG. 46, the gas supply valve 571 is opened and closed with a short period (e.g., 0.1 to 1.0 second). Therefore, the gas is intermittently supplied into the gas pocket 560, and as a result, a flow rate of the two-fluid mixture varies periodically. A jet of the two-fluid mixture that is pulsating in this manner is delivered onto the surface of the substrate, thereby removing the abrasive grains and the polishing debris from the surface of the substrate.
When the gas supply valve 571 is periodically opened and closed, the flow rate of the two-fluid mixture formed in the mixing chamber 561 is expected to pulsate in accordance with a flow rate of the gas as well. However, when the gas supply valve 571 is opened and closed with a short period, an amplitude of the flow rate of the two-fluid mixture becomes smaller than expected, as shown in FIG. 47, due to a residual pressure existing in the gas pocket 560. As a result, a cleaning performance of the two-fluid jet is lowered.
FIG. 48 is a schematic view showing a droplet of the two-fluid mixture. As shown in FIG. 48, the droplet, which constitutes the two-fluid jet, typically has a size of several tens of μm, while fine particles on the substrate W have a size of at most 100 nm. Therefore, as shown in FIG. 49, the droplet cannot enter recesses (e.g., stepped portions of patterns and scratches) formed on the substrate surface, and as a result, cannot remove the fine particles existing in these recesses.
The two-fluid cleaning apparatus has an advantage that a back contamination of the substrate W does not occur, because a cleaning tool, such as a brush or a sponge, is not brought into contact with the substrate W. However, it is difficult for such cleaning apparatus using only the two-fluid jet to sufficiently remove the particles attached to the surface of the substrate W. In particular, the two-fluid jet cannot remove the fine particles existing in the recesses (e.g., stepped portions of patterns and scratches) formed on the substrate surface.